Optical projection array exposure system

ABSTRACT

A spatial light modulator imaging system is disclosed. The system comprises an illumination module configured to provide illumination light representing data patterns to be imaged by the spatial light modulator imaging system, a projection module configured to project the illumination light to a substrate, and an illumination-projection beam separator coupled between the illumination module and the projection module, where the illumination-projection beam separator is configured to receive the illumination light along an illumination optical axis and transmit the illumination light received to the projection module along a projection optical axis, and where the illumination optical axis and the projection optical axis are substantially parallel to each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/909,076 (APPM/22576), filed Jun. 4, 2013, which claimsbenefit of U.S. Provisional Patent Application Ser. No. 61/655,475(APPM/22576L), filed Jun. 4, 2012, each of which is herein incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to the field of lithography manufacturing.In particular, the present invention relates to a maskless digitalprojection exposure system.

SUMMARY

The present disclosure describes embodiments of a maskless digitalprojection exposure system. In one embodiment, the system comprises anillumination module configured to provide illumination lightrepresenting data patterns to be imaged by the spatial light modulatorimaging system, a projection module configured to project theillumination light to a substrate, and an illumination-projection beamseparator coupled between the illumination module and the projectionmodule, where the illumination-projection beam separator is configuredto receive the illumination light along an illumination optical axis andtransmit the illumination light received to the projection module alonga projection optical axis, and where the illumination optical axis andthe projection optical axis are substantially parallel to each other. Inone embodiment, a frustrated cube assembly is disclosed. The frustratedcube assembly includes a first prism, a second prism, a third prism, anda tilted mirror. The first prism includes a first surface, a secondsurface and a first hypotenuse. The second prism includes a thirdsurface, a fourth surface and a second hypotenuse. The first hypotenuseand the second hypotenuse are facing one another and are separated by anair gap. The tilted mirror is adjacent the second surface and the tiltedmirror and the second surface are spaced apart by an air gap.

In another embodiment, a method of forming a spatial light modulatorimaging system comprises providing an illumination module to provideillumination light representing data patterns to be imaged by thespatial light modulator imaging system, providing a projection module toproject the illumination light to a substrate, and providing anillumination-projection beam separator coupled between the illuminationmodule and the projection module, where the illumination-projection beamseparator is configured to receive the illumination light along anillumination optical axis and transmit the illumination light receivedto the projection module along a projection optical axis, where theillumination optical axis and the projection optical axis aresubstantially parallel to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned features and advantages of the invention, as well asadditional features and advantages thereof, will be more clearlyunderstandable after reading detailed descriptions of embodiments of theinvention in conjunction with the following drawings.

FIG. 1 is a perspective view of a system that may benefit fromembodiments disclosed herein.

FIG. 1A illustrates an exemplary spatial light modulator (SLM) imagingunit according to embodiments of the present disclosure.

FIG. 1B illustrates an exemplary overview of optical paths in thespatial light modulator (SLM) imaging unit of FIG. 1A according toembodiments of the present disclosure.

FIG. 2A illustrates an exemplary two dimensional view of anillumination-projection beam separator according to embodiments of thepresent disclosure.

FIG. 2B illustrates an exemplary three-dimensional view of theillumination-projection beam separator of FIG. 2A according toembodiments of the present disclosure.

FIG. 2C illustrates another exemplary three-dimensional view of theillumination-projection beam separator of FIG. 2A according toembodiments of the present disclosure.

FIG. 3 illustrates another exemplary illumination-projection beamseparator according to embodiments of the present disclosure.

FIG. 4 illustrates a plot of RMS wavefront error vs. +Y field for a 1×projection optics according to embodiments of the present disclosure.

FIG. 5 illustrates exemplary 6× projection optics cross-sectionaccording to embodiments of the present disclosure.

FIG. 6 illustrates a plot of RMS wavefront error vs. +Y field for the 6×projection optics of FIG. 5 according to embodiments of the presentdisclosure.

FIG. 7 illustrates exemplary 6× camera optics according to embodimentsof the present disclosure.

FIG. 8 illustrates a plot of RMS wavefront error vs. +Y field for the 6×camera optics of FIG. 7 according to embodiments of the presentdisclosure.

FIG. 9 illustrates a method of forming a spatial light modulator imagingsystem according to some embodiments of the present disclosure.

DESCRIPTION OF EMBODIMENTS

The following descriptions are presented to enable any person skilled inthe art to make and use the invention. Descriptions of specificembodiments and applications are provided only as examples. Variousmodifications and combinations of the examples described herein will bereadily apparent to those skilled in the art, and the general principlesdefined herein may be applied to other examples and applications withoutdeparting from the spirit and scope of the invention. Thus, the presentinvention is not intended to be limited to the examples described andshown, but is to be accorded the widest scope consistent with theprinciples and features disclosed herein.

For a production-worthy maskless projection exposure system, throughputhas to be at least comparable to a mask-based lithography system. Asmentioned, the small SLM imaging unit size limits the size of eachexposure area so that a scanning system is necessary to compose theentire mask pattern. The scanning speed can be determined by severalfactors including the bandwidth of the pattern data pipe that feeds theSLM imaging unit, the mirror pixel tilt and settling time, the exposingscheme, the illumination intensity, etc. Regardless of how the SLMimaging unit exposure is done, a single SLM imaging unit may not beconfigured to match the throughput of mask-based lithography system.However, if multiple SLM imaging units are arranged in an array andconfigured to share the exposure load in parallel, then the system canbe configured to achieve throughputs many times better than aconventional mask-based exposure system. Configuring multiple SLMimaging units into one maskless exposure system is accomplished bytaking advantage of the much smaller scale of the projection andillumination optics that enable maskless exposure. In a conventionalmask-based exposure system, the optical field of view size must betailored to accommodate the entire mask area, and this leads to a verylarge optical system where the cost of the materials for the opticsalone can be more than an order of magnitude greater than thecorresponding cost for an array of SLM columns.

For multiple SLM imaging units configured in an array, each unit isdesigned to be physically compact in order to achieve a densely packedarray formation. This compact footprint design makes it difficult to usethe traditional mercury arc lamp as the illumination source due to thelarge physical size of the traditional mercury arc lamp and the need forheat dissipation. A better alternative design is to use solid-statediode lasers. By attaching an optical fiber to the lasing end of diodelaser, an efficient propagation of pulsed laser light via the opticalfiber is achieved. By bundling a group of such laser-fibers, operatingat a sum of 10 Watts of total laser power, the design can be configuredto have a compact illumination source that delivers sufficient intensityat the imaging plane for the SLM imaging unit. If a mercury arc lampwere used, the inherent brightness of the arc would limit the usefulpower obtained to a much lower value.

In addition to using a compact and efficient illumination source, theSLM imaging unit is designed to accommodate a reflective spatial lightmodulator and to minimize the light loss in the path from the laserdiodes to the substrate. This is done by folding the light pathimplemented in the illumination-projection beam separator, so that lightincident on the surfaces forming the air gap either exceeds the criticalangle, and therefore is totally reflected, or is substantially under thecritical angle, and is therefore efficiently transmitted across the airgap.

To configure a number of SLM imaging units into a tight array suited formaking synchronized exposures, each unit may be designed with a compactfootprint so it can be placed close to its adjacent SLM imaging units.In a projection array exposure system, exposures at each SLM imagingunit may be performed independently and in concert in order to composethe entire substrate pattern. The pattern data may be divided among theSLM imaging units and then be fed to the respective SLM imaging unit forthe exposure. In one approach, the optical path for each of SLM imagingunit may be designed so that it can be readily configured and integratedinto a dense exposure system array that includes multiple SLM imagingunits.

FIG. 1A illustrates an exemplary spatial light modulator (SLM) imagingunit according to embodiments of the present disclosure. According toembodiments of the present disclosure, for each SLM imaging unit tofunction independently, multiple optical modules are used to supporteach SLM imaging unit. As shown in FIG. 1, SLM imaging unit 100 includesthe illumination module 102, illumination-projection beam separator 104,projection module 106, and optionally the camera module 108. Theillumination module 102 includes an exposure source with sufficientintensity for the intended exposure wavelength and a kaleido or lightpipe to achieve uniform illumination over the SLM imaging area. Theprojection module 106 is configured to image pattern data onto thesubstrate. The optical path of the projection module 106 can beconfigured to be in-line (also referred to as parallel) with the mainoptical path of the illumination module 102 in order to form a compactfootprint of the unit. That is, the illumination module 102 andprojection module 106 can be constructed in a slim vertical form. Thecamera module 108 is configured to monitor various aspects of imagingquality of the SLM imaging unit 100, including but not limited to, focusand alignment through the lens as well as to serve as a check SLM mirroron-off behavior. Thus the camera module 108 can be configured to enablemaintenance of the SLM imaging unit and to provide useful exposurevariation diagnostics. In one implementation, the camera module 108 maybe located in the back and towards the sides of each SLM imaging unit.Thus the SLM imaging unit can be made narrow from left to right andmultiple columns can be readily packed into a compact, single-rowconfiguration. If required the next row of SLM imaging units can beplaced at a predetermined distance apart, to accommodate the extra roomrequired by the camera module(s) 108.

FIG. 1B illustrates an exemplary overview of optical paths throughvarious portions of the path from the light pipe to the substrate.Various parts of the optical path are shown with different partitions,namely 131, 132, 133, 134, and 135. Key components of each of thepartitions are shown. A detailed list of the surfaces/components isprovided in Table 1 below. Table 1 describes a list of components usedto form the SLM imaging unit of FIG. 1A and FIG. 1B according toembodiments of the present disclosure.

TABLE 1 SURFACE DATA SUMMARY (Units in Millimeters) Surf Type RadiusThickness Glass Diameter Conic OBJ STANDARD Infinity 76.99117 23.50306 01 STANDARD Infinity 1 SUPRASIL 25.19697 0 2 STANDARD Infinity 2 25.211940 3 STANDARD −290.2887 6 S-LAH66 25.2499 0 4 STANDARD −116.4027 115.91125.53362 0 5 STANDARD 40.37407 4 S-FPL51 15.58083 0 6 STANDARD 139.93831 14.93458 0 7 STANDARD Infinity 30 S-BSL7 14.75115 0 8 STANDARDInfinity 18.69801 10.27299 0 9 STANDARD 26.74097 9 S-FPL51 5.951097 0 10STANDARD −20.4683 5 S-NSL5 3.964418 0 11 STANDARD 17.42661 2.9793482.835765 0 12 STANDARD Infinity 2.979348 2.125411 0 13 STANDARD−17.42661 5 S-NSL5 2.849918 0 14 STANDARD 20.4683 9 S-FPL51 3.97673 0 15STANDARD −26.74097 39.13236 5.960703 0 STO STANDARD −139.9383 4 S-FPL5114.89528 0 17 STANDARD −40.37407 115.6297 15.5402 0 18 STANDARD 116.40276 S-LAH66 25.41056 0 19 STANDARD 290.2887 43.97204 25.1267 0 20 STANDARDInfinity 13 S-BSL7 24.15147 0 21 COORDBRK — 0 — — 22 STANDARD Infinity 0MIRROR 32.16165 0 23 COORDBRK — 0 — — 24 STANDARD Infinity −27 S-BSL723.9619 0 25 STANDARD Infinity −0.5 23.5682 0 26 STANDARD Infinity−2.997 S-FSL5 23.55704 0 27 STANDARD Infinity −0.483 23.51244 0 28STANDARD Infinity 0 23.50462 0 29 DGRATING Infinity 0 MIRROR 23.50462 030 STANDARD Infinity 0.483 23.50462 0 31 STANDARD Infinity 2.997 S-FSL523.93682 0 32 STANDARD Infinity 0.5 25.63359 0 33 STANDARD Infinity 40S-BSL7 26.08404 0 34 STANDARD Infinity 0 48.67878 0 35 DGRATING Infinity0 MIRROR 48.67878 0 36 STANDARD Infinity 0 24.78373 0 37 STANDARDInfinity −21.628 S-BSL7 24.78373 0 38 COORDBRK — 0 — — 39 STANDARDInfinity 0 MIRROR 33.63665 0 40 COORDBRK — 0 — — 41 STANDARD Infinity18.372 S-BSL7 25.10212 0 42 STANDARD Infinity 15 25.37257 0 43 COORDBRK— 0 — — 44 STANDARD Infinity 0 MIRROR 34.57223 0 45 COORDBRK — −30 — —46 COORDBRK — 0 — — 47 STANDARD Infinity 0 MIRROR 35.48185 0 48 COORDBRK−21.231 — — 49 STANDARD −103.6759 3.5 S-FPL51 26.84381 0 50 STANDARD−51.87603 149.7883 27.10744 0 51 STANDARD 16.52846 2.5 S-LAL13 8.8293170 52 STANDARD 12.23028 0.6516637 8.05797 0 53 STANDARD 29.92611 3S-FPL53 8.052902 0 54 STANDARD −40.07405 23.854 7.803958 0 55 STANDARDInfinity 2.1 2.887609 0 pupil 56 STANDARD 25.89648 2 PBM18Y 3.206145 057 STANDARD 6.411588 2 S-FPL53 3.299604 0 58 STANDARD −15.94908 5.1522013.493134 0 59 STANDARD 4.910884 2 S-FPL53 3.874677 0 60 STANDARD−143.7341 0.1 3.532434 0 61 STANDARD 3.690008 2 S-FPL51 3.364643 0 62STANDARD 2.949571 1.8 S-NBM51 2.354322 0 63 STANDARD 1.91234 0.59351.399212 0 IMA STANDARD Infinity 1.20883 0 kaleido

According to embodiments of the present disclosure, to controlimaging/printing resolution, the image projection objective can bedesigned with an appropriate reduction factor. However, one challenge ofincreasing the reduction factor is that it reduces the exposure area ina quadratic fashion. This may negatively impact the exposure throughputand may substantially increase the number of pixels to be manipulated tocreate the data fed to the DMD. For printed circuit board (PCB)lithography, the printing resolution may be above 20 um. Hence a 1×SLMimaging unit described in the following sections with no objectivereduction may be adequate, given that the native DMD mirror pixeldimension may be about 10.8 um. This scale factor can also help toensure sufficient exposure throughput. For the LED and TSV applications,the minimum critical dimension (CD) for typical design rules may be inthe range from 3 to 5 um. In this case, a 6× projection optical designdescribed in the following sections may be employed since the printedDMD mirror dimension may be around 3 um. For these applications,multiple SLM imaging units arranged in an array configuration are usedto meet the desired throughput.

According to aspects of the present disclosure, a 1× objective designand a 6× reduction objective design may be employed. Note that a widevariety of magnifications, both larger or smaller than the 1× or the 6×design, can be configured to work with the present disclosure. Bothdesigns can be configured to share a common illumination module 102. Forease of focus and alignment, the projection objective may be designedwith a common focus for all the actinic exposure wavelengths as well asthe selected non-actinic wavelengths, which typically extend into thevisible and sometimes into the infrared part of the spectrum.Additionally, a programmable focus stage can be mounted on the body ofeach SLM imaging unit to enable auto focusing, which allows the DMDimage to follow the substrate surface during the exposure.

According to aspects of the present disclosure, the system is designedso that the illumination fill factor, can be monitored for everymicro-mirror in the DMD array. That is, the tilt angle of eachmicro-mirror, which varies from on to off or from −12 degrees to +12degree, can be checked to ensure that the on-position delivers the lightincident on the mirror to the nominal center of the projection systempupil and the off-position removes most of the light incident on themirror from the projection system pupil. The manufacturersspecifications indicates that the mirror tilt angle can vary as much as±1 degree. This means that the direction of the beam reflected from themicro-mirror may vary by as much as two degrees. This variation wouldshift the reflected illumination beam toward the projection system pupiledge, but most of the light would still pass through the projectionsystem. Thus the use of a relatively small illumination fill factorensures that the design can accommodate this mirror tilt variation. Analternate approach to reduce the sensitivity to mirror tilt angle is todesign an illumination module 102 that over-fills the projection lenspupil. Underfilling the projection pupil with an illumination numericalaperture (NA) that is smaller than the projection NA is more efficientand is often referred to as employing partially coherent illumination.The partial coherence factor (a) can be expressed as follows:

σ=(NA of the illumination)(NA of the imaging objective)

When the NA of the illumination is the same as the NA of the objective,the σ is 1. Overfilling means that the σ is greater than 1. When σ is 1or greater, the illumination is described as incoherent, and theresultant image is wider and exhibits less ringing beyond the first nullpoint. For some lithography imaging applications, one approach is tohave σ.apprxeq.0.5. This is because some degree of optical ringing isoften desirable when a high contrast resist system is employed. Thesteeper image profile near the exposure threshold level results inbetter line-width control and the more pronounced ringing falls wellbelow the threshold level and is not seen in the developed image. In thedisclosed SLM imaging unit, a low σ factor from 0.25 to 0.27 is chosento achieve a better resultant aerial image profile under the conditionstypically employed where multiple pixels having an almost randomlocation are superimposed. This approach may be counter-intuitive,especially when diode lasers are used as the illumination source. Unlikeconventional mercury arc lamp or LED light sources, the laser lightsource can be highly coherent in nature. It may have the tendency tocause laser speckles that may render the distribution of light in theimaging plane to be non-uniform. With more coherent illumination, or asmaller value of σ, the non-uniformity could become worse. According toaspects of the present disclosure, the use of an illumination systemhaving a low σ factor can be used in conjunction with pixel blending,which is a method of imaging together superimposed pixels for patterningfeatures. This approach, not only achieves a better image edge profile,it also reduces the negative effects of mirror tilt angle errors.According to the embodiments of the present disclosure, one solution isto make use of a low σ illumination design together with diode laserillumination source; and to employ an exposure imaging process thatincludes superimposing multiple pixels so as to average the exposuredose over several pixels.

The illumination module 102 includes multiple laser diodes, which areoptically coupled via a fiber bundle to one end of a kaleido, which letsalmost all of the input light propagate to the other end. Having gonethrough ten or more total internal reflections inside the kaleido, theoutput laser illumination has been folded multiple times so as to form auniform intensity distribution across the kaleido output face. Thekaleido is mounted and centered in a fixture while retaining the totalinternal reflection (TIR) property that prevents light from leaking outof the kaleido sides. In order to minimize any light leak, objects thatmay touch one of the sides of the kaleido are minimized because they maycause an appreciable light leak.

Materials that can be used to touch the kaleido side are selected tosatisfy the TIR formula shown below. Here the NA refers to incomingfiber output numerical aperture, which may typically be about 0.22. N1refers to the refraction index of the kaleido, which may be made offused silica having a refraction index near 1.47 at approximately 405 nmwavelength. The formula predicts that the refractive index of theselected material, N2 that can safely touch the kaleido, can have arefraction index below 1.45 at approximately 405 nm. Teflon film such asFEP and an inorganic MgF2 coating material have this property andtherefore may be suitable for this application. The NA may be computedwith the following mathematical expression:

NA≦√(

N1

{circumflex over (0)}2−

N2

{circumflex over (0)}2)

According to aspects of the present disclosure, one approach is to use aholder that sandwiches a kaleido between two sheets of about 5 mil FEP(Teflon) film using a pair of grooved metal jaws, which can be tightenedwith screws to hold the kaleido firmly. The FEP film “cladding” may beused because its refractive index is low enough to maintain a totalinternal reflection. Other embodiments may include pre-coating thekaleido with a low index material to ensure internal reflection, thengripping it without damaging the sub-surface of the coating. For thecoating material, it may be FEP Teflon or MgF2. The coating can be thickenough to allow some margin of error without significant loss ofreflectivity. For example, the coating thickness can be set to exceed atleast 10 exposure wavelengths. Instead of coating the kaleido, anotherapproach is to coat the sides of the holding fixture with severalmicrons of Teflon film.

The following paragraphs describe two types of projection module 106designs, one with a 1× magnification in the projection system, thesecond with a 6× magnification projection system that reduces the mirrorpixel size of approximately 10.8 um by 6 times to approximately 1.8 umon the substrate. FIG. 1A and Table 1 above describe an exemplaryimplementation of the 1× optical system including the illuminationmodule 102 and projection module 106. The 6× system may share a commonillumination module 102 with the 1× system. The projection module 106 isfurther described in FIG. 5 and Table 2. An example of the camera module108 is illustrated in FIG. 7 and described in Table 3. The following isa summary of the design data.

The basic optical system parameters can be summarized as shown:

1X Projection 6X Projection Working distance  76.99 mm  6 mm OverallLength 542.27 mm 386 mm Object NA .04 0.24 Image NA .04 0.04

Both designs can be configured to be doubly telecentric that have verylow distortion across the field (i.e. much less than 0.1%), and may bewell corrected at approximately 400 nm, 405 nm, 410 nm, and 633 nm. The1× design may also be corrected at approximately 550 nm, which is theintended alignment wavelength for this system, whereas the 6× system iscorrected at approximately 940 nm for alignment. The exposure radiationspectrum can be in the 400-410 nm part of the spectrum, which explainswhy there are 3 corrected wavelengths in this band. The lens can bebuilt and adjusted using a phase measurement interferometer operating atthe HeNe laser wavelength at 6328 Angstroms. Note that in some cases thecorrected wavelength range spans more than a factor of 2 and the glassesmay be chosen based on the specific design criteria. For example, in the1× case, the wavefront correction can be approximately 0.05 waveroot-mean-square (RMS) or better from 380 nm to 1050 nm, which is abouta factor of 3 in wavelength span. See FIGS. 4, 6, and 8. Note that onefeature of both designs is that they maintain a flat window between theimage plane and the first lens element. This is done in anticipationthat the window may eventually become coated with residue resulting fromthe vapors released during the resist exposure process and they may bereplaced and serviced.

According to aspects of the present disclosure, telecentricity on theimage side of the lenses is implemented in the disclosed design in orderto prevent small magnification changes with focal position. Althoughtelecentricity may not be required on the object side, it can simplifythe illuminator design and improve performance and illuminationuniformity from the digital micro-mirror devices.

Note that some lithography applications may require substantiallyprecise superposition of many different patterns, often imaged bydifferent lithography tools. This overlay accuracy can be a smallfraction of the minimum feature size, so variations in distortion fromone lithography tool to another can consume the entire overlay budgetleaving nothing for the alignment budget. Thus in addition to keepingthe distortion very low across the field in the exposure part of thespectrum, the disclosed implementation may also be configured to keepdistortion small at the alignment wavelength, which is usually locatedat the other end of the spectrum. Another reason the disclosed design isimplemented with low distortion is to support seamless image stitchingbetween the adjacent SLM imaging units. According to embodiments of thepresent disclosure, both the 1× and 6× designs may share a commonillumination module and an illumination-projection beam separatorlocated adjacent to the micro-mirror array (also referred to as aDigital Micro-mirror Device (DMD)).

FIG. 2A illustrates an exemplary optical path in anillumination-projection beam separator according to embodiments of thepresent disclosure. As shown in FIG. 2A, the illumination-projectionbeam separator 104 can be formed with two prisms 202 and 204 arrangedwith the hypotenuse surfaces facing each other and with a very small airgap 206 between them, for example in the range of 0.005 to 0.015millimeter. One surface of the prism 202 may be attached to a beamorientation adjustor 208, which may be implemented as a reflectivegrating surface. Light incident on the air gap surfaces at 45 degrees isreflected at 90 degrees to its original direction. Light incident on theair gap surfaces at an angle closer to normal incidence passes throughthe air gap 206 without being reflected. In one approach, theillumination-projection beam separator 104 is arranged so that lightfrom the illumination module 102 that is directed at the micro-mirrorarray 210 (also referred to as digital micro-mirror device) at about 24degrees from normal incidence in air hits the S-BSL7 glass-air gapsurfaces at an incidence angle below the critical angle of 40.81° andtherefore passes through the gap un-deviated. Light reflected from themicro mirror array 210 at near normal incidence strikes the air gapsurfaces at about 45 degrees and is therefore configured to be reflectedalong the projection module optical axis. Thus theillumination-projection beam separator 104 separates the incidentillumination beam from the reflected projection system beam with highefficiency and without taking very much space.

According to aspects of the present disclosure, a smaller footprint maybe achieved by making the illumination module optical axis and theprojection module optical axis substantially parallel to each other. Oneimplementation is to apply a beam orientation adjustor 208, which may beimplemented as a reflective grating surface to the surface opposite theDMD. As a result, the illumination-projection beam separator 104 foldsthe illumination module optical axis to be substantially parallel to theprojection module optical axis. In addition, the illumination-projectionbeam separator 104 straightens out the DMD focal plane tilt. The gratingperiod and diffraction order can be selected to generate anapproximately 24° incidence angle in air in one implementation of theDMD 210. The mirrors on the DMD pivot in an azimuth plane rotated about45° with respect to the section shown, and the rows and columns ofmirrors on the DMD surface. The design is configured to rotate thegrating surface about the Y-axis so the light diffracted from the mirrorgrating is diffracted at a compound angle in the space between thereflective grating and the DMD 210. In other implementations, the DMD210 can also be represented as a rotated grating, which then restoresthe direction of the optical axis. Note that in yet otherimplementations, the beam orientation adjustor 208 may be configured toaccommodate different incidence angles (such as 22°, 26°, 28°, etc.) tothe DMD 210.

FIG. 2B illustrates an exemplary three-dimensional view of theillumination-projection beam separator of FIG. 2A according toembodiments of the present disclosure. As shown in FIG. 2B, the incomingillumination beam is incident on surface 212 at normal incidence and istransmitted directly to surface 214, which is oriented at 45° to theincoming beam and which has an air gap 206 on the other side.Consequently the incident beam is totally reflected from the air gap 206and is incident on surface 216 at normal incidence. Surface 216incorporates beam orientation adjustor 208 (not shown), which may beimplemented as a blazed, reflective grating on its surface with linesoriented at 45° to the X or Z axis, and with a grating period and blazedirection oriented so that most of the incident light is diffracted atan angle to the normal equal to twice the tilt angle of DMD 210 and inthe same plane of incidence as the tilt angle of DMD 210. Afterdiffraction from the grating on surface 216, the beam is again incidenton surface 214, the hypotenuse surface, only this time the incidentangle on surface 214 is less than the critical angle so the beam istransmitted through surface 214 and also surface 218 and leaves theprism 204 through surface 220, after which it is incident on the DMD210. Since the beam is incident on the DMD 210 at the right incidentangle (for example approximately 24°) and in the same plane as themicro-mirror on-tilt angle, it is reflected normal to the DMD 210 andenters surface 220. After surface 220, the beam is incident of surface218, but at an angle exceeding the critical angle so it is reflectedfrom surface 218 and passes through surface 222 along the optical axisof the projection module 106. FIG. 2C illustrates another exemplarythree-dimensional view of the illumination-projection beam separator ofFIG. 2A according to embodiments of the present disclosure.

An alternate configuration that achieves much the same effect as thearrangement shown in FIG. 2A is shown in FIG. 3. As shown in FIG. 3, theincoming illumination beam is incident on surface 312 of prism 302 atnormal incidence and is transmitted directly to surface 314, which isoriented at 45° to the incoming beam and which has an air gap 306 on theother side. Consequently the incident beam is totally reflected from theair gap 306 and is incident on surface 316 at normal incidence. Surface316 incorporates beam orientation adjustor 308, which may be implementedas a wedge mirror with lines oriented at 45° to the X or Z axis, andwith a direction oriented so that most of the incident light isdiffracted at an angle to the normal equal to twice the tilt angle ofDMD 310 and in the same plane of incidence as the tilt angle of DMD 310.After reflection from the mirror on surface 316, the beam is againincident on surface 314, the hypotenuse surface, only this time theincident angle on surface 314 is less than the critical angle so thebeam is transmitted through surface 314 and also surface 318 and leavesthe prism 304 through surface 320, after which it is incident on the DMD310. Since the beam is incident on the DMD 310 at the right incidentangle (for example approximately 24°) and in the same plane as themicro-mirror on-tilt angle, it is reflected normal to the DMD 310 andenters surface 320. After surface 320, the beam is incident of surface318, but at an angle exceeding the critical angle so it is reflectedfrom surface 318 and passes through surface 322 along the optical axisof the projection module 106.

In the example shown in FIG. 3, the beam orientation adjustor 208(implemented as the blazed, reflective grating on surface 216) isreplaced by a wedge mirror 308 oriented so that the steepest slope is at45° to the X and Z-axis of FIG. 3. Thus the beam paths are substantiallysimilar in FIGS. 2A and 3A and the beams are incident on the DMD 310 atidentical compound angles.

In other implementations, the mirror surface on surface 316 can beincorporated into the piece forming the prism 302 or it can be added byattaching a thin wedge shaped mirror 308 to prism 302 as indicated bythe dotted line in FIG. 3. Note that a person of ordinary skill in theart may appreciate that FIGS. 2A-2C and FIG. 3 are schematics intendedto illustrate exemplary designs and may not be perfectly accuraterepresentations of the path a light ray may travel through the manyair-glass interfaces. In some cases the change of angle that occurs atan air-glass interface may not have been described.

Although the technique described above allows the tracing of rays fromthe end of the light pipe to the image plane of the projection module,the optical design program can be configured to handle one color at atime. Changing wavelength may be desirable such that the grating periodsmay also be changed. An alternative representation of both the DMD 210and the reflective grating 208 may be a blazed, flat, Fresnel mirrorwith each facet equal to the size of a micro-mirror in the array, whichis about 10.8 microns. One approach to implement this design is toreplace the rotated, reflective grating with a flat mirror surfaceoriented at a compound angle such that the illumination axis may bereflected at an azimuth angle and incidence angle compatible with theDMD tilt mirrors.

Note that the illumination-projection beam separator 104 can introduceabout 40 mm of glass on the projection side and about 80 mm of glass onthe illumination side of the system. The NA may be low in this space sothat the color that comes with converging beams and thick pieces ofglass may be corrected.

According to aspects of the present disclosure, the 1× system isconfigured to be a substantially symmetrical system having a pupillocated in the center between two doublets. This system has almost nocoma or distortion because of the symmetry. In the event if symmetry maybe compromised because of the introduction of theillumination-projection beam separator 104, a beam-splitter may beconfigured to extract light for alignment, and the window may be used toprotect the rest of the optical train. In one implementation, a workingdistance of approximately 77 mm may be achieved with this design form.

The illumination module 102 may be substantially similar for both the 1×and 6× implementations of the projection module 106. It includes acompact 10× objective and a field lens, and produces a 0.011 NA,telecentric, and illumination field at the DMD. This NA may beconsiderably smaller than the 0.04 NA of the 1× and 6× projectionsystems resulting in a partial coherence factor of 0.275. This improvesthe slope of the image profile and improves the depth-of-field. Inaddition, it may be more forgiving of angular tilt errors in themicro-mirror array. Such an error tends to move the center of theillumination beam away from the center of the projection system pupil.To address the above issue, the design is configured to make theprojected illumination pupil small with respect to the projection pupil,such that a larger deviation can be tolerated before vignettingcompromises the image illumination uniformity. The illumination module102 also includes two folding mirrors that considerably reduce theoverall length to about 148 mm from the input end of the light pipe tothe illumination-projection beam separator 104.

Note that the approximately 0.22 NA at the light pipe end of theilluminator relay may be available for fiber coupled laser diodes. ThisNA may be able to enable a reasonable number of bounces in order tohomogenize the light at the output end. With this approach, the highmagnification of the relay sets the cross-section size of the light pipeto about 2.1 mm by 1.2 mm.

With respect to the camera module 108, where the correction wavelengthsmay remain substantially the same as for the projection module 106, thefield diameter can be approximately 6 mm, and the NA can beapproximately 0.16. Note that in some implementations, the 1×SLM imagingunits may be stacked close together in a single row that spanned thewidth of the substrate. This allows the camera module 108 to extend in adirection orthogonal to the projection module optical axis as far asneeded without additional folds. In some other implementations, the6×SLM imaging units may be stacked into a two-dimensional array and theoptical path for the camera module 108 may be constrained. One solutionis to use another folding prism right after the beam-splitter thatseparates the optical path of the camera module 108 from the opticalpath of the projection module 106. This can be accomplished by placingthe beam-splitter in part of the optical path that is collimated so theeffect on axial color can be minimized. A correction of about 0.03lambda RMS may be achieved at the specified wavelengths for the 6×design.

FIG. 4 illustrates a plot of RMS wavefront error vs. +Y field for a 1×projection optics according to embodiments of the present disclosure. Inthe example shown in FIG. 4, the horizontal axis represents +Y field inmillimeters in the range from 0 to 12 millimeters. The vertical axisrepresents RMS wavefront error in waves in the range from 0 to 0.020.The RMS wavefront errors of the colors are shown. For example, curve 402represents color blue, curve 404 represents color red, curve 406represents color indigo, curve 408 represents color green, curve 410represents color orange, and curve 412 represents color violet.

FIG. 5 illustrates exemplary 6× projection optics cross-sectionaccording to embodiments of the present disclosure. As shown in FIG. 5,various optical components are shown. A detailed list of the componentsis provided in Table 2 below. Table 2 describes the components of the 6×projection optics of FIG. 5 according to embodiments of the presentdisclosure.

TABLE 2 SURFACE DATA SUMMARY: Surf Type Radius Thickness Glass DiameterConic Comment OBJ STANDARD Infinity 6 3.999985 0 1 STANDARD Infinity 1SUPRASIL 6.966693 0 2 STANDARD Infinity 2 7.302071 0 3 STANDARD−11.63312 14.94394 S-LAH65 7.945194 0 4 STANDARD −40.91397 0.1 16.779340 5 STANDARD −46.77722 2.5 S-BSM18 16.92844 0 6 STANDARD 42.02167 5S-FPL53 19.56794 0 7 STANDARD −25.9494 0.1 20.87682 0 8 STANDARD391.3741 3.5 S-FPL53 22.72886 0 9 STANDARD −41.99294 0.1 23.52602 0 10STANDARD 52.45408 4 S-FPL53 24.96397 0 11 STANDARD −64.44142 0.125.13682 0 12 STANDARD 43.40388 3.5 S-FPL53 25.20843 0 13 STANDARD−107.849 0.1 25.0551 0 14 STANDARD 28.86787 5 S-FPL53 23.83517 0 15STANDARD −122.2302 2 SUPRASIL 22.85031 0 STO STANDARD 17.85497 45.57220.00163 0 17 STANDARD Infinity 25 SUPRASIL 14.21682 0 18 STANDARDInfinity 10.62439 16.40614 0 19 STANDARD 276.6007 5 S-FPL53 17.77596 020 STANDARD −23.34284 4 S-BAL41 17.98696 0 21 STANDARD −79.7 156.721418.65613 0 22 STANDARD 203.1093 3.5 S-FTM16 29.64208 0 23 STANDARD67.36893 6 S-LAH55 29.58431 0 24 STANDARD 517.8979 35.65827 29.26589 025 STANDARD Infinity 40 S-BSL7 26.38255 0 26 STANDARD Infinity 0.524.25776 0 27 STANDARD Infinity 2.997 S-FSL5 24.21709 0 28 STANDARDInfinity 0.483 24.05461 0 IMA STANDARD Infinity 24.02078 0

FIG. 6 illustrates a plot of RMS wavefront error vs. +Y field for the 6×projection optics of FIG. 5 according to embodiments of the presentdisclosure. In the example shown in FIG. 6, the horizontal axisrepresents +Y field in millimeters in the range from 0 to 12millimeters. The vertical axis represents RMS wavefront error in wavesin the range from 0 to 0.050. The RMS wavefront errors of the colors areshown. For example, curve 602 represents color blue, curve 604represents color violet, curve 606 represents color indigo, curve 408represents color orange, curve 610 represents color red, and curve 612represents color green.

FIG. 7 illustrates exemplary 6× camera optics according to embodimentsof the present disclosure. As shown in FIG. 7, various opticalcomponents are shown. A detailed list of the components is provided inTable 3 below. Table 3 describes the 6× camera optics of FIG. 7according to embodiments of the present disclosure.

TABLE 3 SURFACE DATA SUMMARY: Surf Type Radius Thickness Glass DiameterConic OBJ STANDARD Infinity 6 3.999957 0 1 STANDARD Infinity 1 SUPRASIL6.966665 0 2 STANDARD Infinity 2 7.302043 0 3 STANDARD −11.6331214.94394 S-LAH65 7.945167 0 4 STANDARD −40.91397 0.1 16.77929 0 5STANDARD −46.77722 2.5 S-BSM18 16.9284 0 6 STANDARD 42.02167 5 S-FPL5319.56788 0 7 STANDARD −25.9494 0.1 20.87678 0 8 STANDARD 391.3741 3.5S-FPL53 22.7288 0 9 STANDARD −41.99294 0.1 23.52596 0 10 STANDARD52.45408 4 S-FPL53 24.96391 0 11 STANDARD −64.44142 0.1 25.13676 0 12STANDARD 43.40388 3.5 S-FPL53 25.20837 0 13 STANDARD −107.849 0.125.05503 0 14 STANDARD 28.86787 5 S-FPL53 23.83512 0 15 STANDARD−122.2302 2 SUPRASIL 22.85026 0 STO STANDARD 17.85497 45.572 20.00159 017 STANDARD Infinity 50 SUPRASIL 14.21682 0 18 STANDARD Infinity 0.118.59543 0 19 STANDARD 51.42428 6 S-FPL51 18.7174 0 20 STANDARD−13.61537 2 SUPRASIL 18.6639 0 21 STANDARD −58.72156 4.016346 18.20835 022 STANDARD −26.85794 4 S-TIM1 17.28783 0 23 STANDARD −12.60856 2S-LAM55 17.45899 0 24 STANDARD −75.4502 7.048056 18.55384 0 25 STANDARD231.0992 4 S-FPL53 20.14024 0 26 STANDARD −26.20011 24.38191 20.3371 027 STANDARD 30.26877 25 S-FSL5 14.71653 0 28 STANDARD 10.80071 1.0975127.289978 0 29 STANDARD 8.250533 2.236983 S-LAL18 7.161331 0 30 STANDARD10.52782 1 6.294749 0 31 STANDARD Infinity 0.4 S-BSL7 6.123171 0 32STANDARD Infinity 0.125 6.036451 0 IMA STANDARD Infinity 6.004747 0

FIG. 8 illustrates a plot of RMS wavefront error vs. +Y field for the 6×camera optics of FIG. 7 according to embodiments of the presentdisclosure. In the example shown in FIG. 4, the horizontal axisrepresents +Y field in millimeters in the range from 0 to 3.0millimeters. The vertical axis represents RMS wavefront error in wavesin the range from 0 to 0.050. The RMS wavefront errors of the colors areshown. For example, curve 802 represents color red, curve 804 representscolor green, curve 806 represents color indigo, curve 808 representscolor violet, curve 810 represents color orange, and curve 812represents color indigo.

FIG. 9 illustrates a method of forming a spatial light modulator imagingsystem according to some aspects of the present disclosure. Certainfunctions of the method may be implemented by one or more processors. Inblock 902, the method provides an illumination module, where theillumination module is configured to provide illumination lightrepresenting data patterns to be imaged by the spatial light modulatorimaging system. In block 904, the method provides a projection module,where the projection module is configured to project the illuminationlight to a substrate. In block 906, the method provides anillumination-projection beam separator coupled between the illuminationmodule and the projection module, where the illumination-projection beamseparator is configured to receive the illumination light along anillumination optical axis and transmit the illumination light receivedto the projection module along a projection optical axis, and where theillumination optical axis and the projection optical axis aresubstantially parallel to each other. Note that, the illumination modulecan be configured to be telecentric with respect to the illuminationlight, and the projection module can be configured to be telecentricwith respect to the substrate.

According to embodiments of the present disclosure, the methodsperformed in block 902 may further include methods performed in block910. Methods performed in block 904 may further include methodsperformed in block 912. Methods performed in block 906 may furtherinclude methods performed in block 914. In block 910, the methodgenerates the illumination light by a plurality of laser diodes,transmits the illumination light to the illumination-projection beamseparator using a plurality of fiber bundles, and holds the plurality offiber bundles using a kaleido. In block 912, the method projects thedata patterns at a one-to-one magnification and/or projects the datapatterns at a six-to-one magnification reduction.

In block 914, the method provides a first prism, a beam orientationadjustor, a digital micro-mirror device (DMD), and a second prism, wherethe beam orientation adjustor is located adjacent to the first prism,the beam orientation adjustor is configured to adjust the illuminationlight to enter the DMD located adjacent to the second prism at apredetermined incidence angle relative to a normal of the DMD, and thepredetermined incidence angle is substantially equal to twice of anangle of tilt of the DMD, and the method separate the first prism andthe second prism with an air gap. In addition, the method receive theillumination light along the illumination optical axis using the firstprism, controls the illumination light to pass through the first prism,the beam orientation adjustor, the air gap, the DMD, and the secondprism, and transmits the illumination light along the projection opticalaxis using the second prism.

According to aspects of the present disclosure, the first prismcomprises a first right angle prism, where the first right angle prismincludes a first surface configured to receive the illumination light atapproximately normal incidence; a second surface configured to receivethe illumination light at approximately 45 degree angle and to cause theillumination light to be substantially reflected at the second surface;a third surface coupled to the beam orientation adjustor, wherein thethird surface and the beam orientation adjustor are configured to causethe illumination light to pass through the second surface and the airgap at the predetermined incidence angle.

According to aspects of the present disclosure, the second prismcomprises a second right angle prism, where the second right angle prismincludes a first surface configured to receive the illumination lightfrom the first prism; a second surface configured to pass theillumination light to the DMD and receive the illumination lightreflected from the DMD; the first surface is further configured tosubstantially reflect the illumination light reflected from the DMD; athird surface configured to transmit the illumination light reflectedfrom the first surface along the projection optical axis. The air gaphas a dimension in a range of 0.005 millimeter to 0.015 millimeter.

According to aspects of the present disclosure, the beam orientationadjustor comprises at least one of a wedge mirror having a thickness ofapproximately 4.67 millimeters at a first end, having a thickness ofapproximately 2.18 millimeters at a second end, and having a slope ofapproximately 5.47°; and a reflective grating coating formed with aninorganic MgF2 coating, having a thickness of larger than ten times of acorresponding exposure wavelength of the spatial light modulator imagingsystem.

According to aspects of the present disclosure, in block 916, the methodmonitors focus and alignment of the spatial light modulator imagingsystem using a camera module, and checks micro-mirror on-off behaviorusing the camera module, where the camera module is configured to betelecentric with respect to the substrate.

It will be appreciated that the above description for clarity hasdescribed embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits or processors may be used without detracting from the invention.For example, functionality illustrated to be performed by separateprocessors or controllers may be performed by the same processors orcontrollers. Hence, references to specific functional units are to beseen as references to suitable means for providing the describedfunctionality rather than indicative of a strict logical or physicalstructure or organization.

The method and system of the present disclosure can be implemented inany suitable form, including hardware, software, firmware, or anycombination of these. The invention may optionally be implemented partlyas computer software running on one or more data processors and/ordigital signal processors. The elements and components of an embodimentof the invention may be physically, functionally, and logicallyimplemented in any suitable way. Indeed, the functionality may beimplemented in a single unit, in a plurality of units, or as part ofother functional units. As such, the invention may be implemented in asingle unit or may be physically and functionally distributed betweendifferent units and processors.

One skilled in the relevant art will recognize that many possiblemodifications and combinations of the disclosed embodiments may be used,while still employing the same basic underlying mechanisms andmethodologies. The foregoing description, for purposes of explanation,has been written with references to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described to explain the principles of theinvention and their practical applications, and to enable others skilledin the art to best utilize the invention and various embodiments withvarious modifications as suited to the particular use contemplated.

What is claimed is:
 1. An illumination-projection assembly, comprising:a first prism, wherein the first prism comprises: a first surface; asecond surface; and a first hypotenuse; and a second prism, wherein thesecond prism comprises: a third surface; a fourth surface; and a secondhypotenuse; wherein the first hypotenuse and the second hypotenuse arefacing one another, and wherein the first hypotenuse and the secondhypotenuse are separated by an air gap.
 2. The illumination-projectionassembly of claim 1, further comprising a digital micro-mirror device,wherein the digital micro-mirror device is adjacent the third surface.3. The illumination-projection assembly of claim 1, wherein the firstsurface and the fourth surface are parallel to one another.
 4. Theillumination-projection assembly of claim 1, wherein the second surfaceand the third surface are parallel to one another.
 5. Theillumination-projection assembly of claim 1, wherein the second surfaceis sloped.
 6. The illumination-projection assembly of claim 1, furthercomprising a beam orientation adjuster, wherein the beam orientationadjuster is a grating surface, and wherein the grating surface is on andin contact with the second surface.
 7. The illumination-projectionassembly of claim 1, further comprising a beam orientation adjuster,wherein the beam orientation adjuster is a wedge mirror, and wherein thewedge mirror is on and in contact with the second surface.
 8. Anillumination-projection assembly, comprising: a first prism, wherein thefirst prism comprises: a first surface; a second surface; a gratingsurface, wherein the grating surface is on and in contact with thesecond surface; and a first hypotenuse; and a second prism, wherein thesecond prism comprises: a third surface; a fourth surface; and a secondhypotenuse; wherein the first hypotenuse and the second hypotenuse arefacing one another, and wherein the first hypotenuse and the secondhypotenuse are separated by an air gap.
 9. The illumination-projectionassembly of claim 8, further comprising a digital micro-mirror device,wherein the digital micro-mirror device is adjacent the third surface.10. The illumination-projection assembly of claim 8, wherein the firstsurface and the fourth surface are parallel to one another.
 11. Theillumination-projection assembly of claim 8, wherein the second surfaceand the third surface are parallel to one another.
 12. Theillumination-projection assembly of claim 8, wherein the grating surfaceis a blazed grating surface.
 13. The illumination-projection assembly ofclaim 8, wherein the grating surface comprises lines oriented at 45° toan X or a Z axis.
 14. The illumination-projection assembly of claim 8,wherein the air gap is between about 0.005 millimeters and about 0.015millimeters.
 15. An illumination-projection assembly, comprising: afirst prism, wherein the first prism comprises: a first surface; asecond surface; a wedge mirror, wherein the wedge mirror is on and incontact with the second surface; and a first hypotenuse; and a secondprism, wherein the second prism comprises: a third surface; a fourthsurface; and a second hypotenuse; wherein the first hypotenuse and thesecond hypotenuse are facing one another, and wherein the firsthypotenuse and the second hypotenuse are separated by an air gap. 16.The illumination-projection assembly of claim 15, further comprising adigital micro-mirror device, wherein the digital micro-mirror device isadjacent the third surface.
 17. The illumination-projection assembly ofclaim 15, wherein the first surface and the fourth surface are parallelto one another.
 18. The illumination-projection assembly of claim 15,wherein the second surface and the third surface are parallel to oneanother.
 19. The illumination-projection assembly of claim 15, whereinthe wedge mirror comprises lines oriented at 45° to an X or a Z axis.20. The illumination-projection assembly of claim 15, wherein the airgap is between about 0.005 millimeters and about 0.015 millimeters.